The present invention relates to a transfer path control system comprising two transfer devices connected to each other through two transfer paths consisting of a main transfer path (working line) and a sub-transfer path (protection line).
A dual transfer system has hither to been proposed in order to ensure a reliability of data transfer paths. The dual transfer system has an architecture, which will hereinafter roughly be explained. To be specific, as shown in FIG. 13(a), two transfer devices 101, 102 are connected to each other through two transfer paths P1, P2. For example, the transfer path P1 is used as a main transfer path, while the transfer path P2 is used sub-transfer path. The transfer device 101 on a transmitting side transmits the same data substantially simultaneously from the transfer paths P1, P2. The transfer device 102 on a receiving side, when receiving through the transfer paths P1, P2 the communications data transmitted from the transfer device 101, transfers only the data received through the transfer path P1 used as the main transfer path toward still another transfer device (not shown) disposed downstream, and discards the data received through the transfer path P2.
For instance, if an accident happens on the transfer path P1, the transfer device 102 is unable to receive the data through the transfer path P1 from the transfer device 101. Then the transfer device 102, as shown in FIG. 13(b), switches the main transfer path from the transfer path P1 to the transfer path P2. The transfer device thereafter, transfers to another transfer device the data received through the transfer path P2. The reliability of the data transfer paths is thereby ensured.
In the example given above, for instance, if the accident occurs on the transfer path P1, the main transfer path is instantaneously switched over from the transfer path P1 to the transfer path P2. It is therefore required that each piece of data transferred through the transfer path P1 and the transfer path P2 be synchronized.
More specifically, if the data transferred through the transfer path P2 is received earlier by the transfer device 102 than the data transferred through the transfer path P1, missing of data might happen when the transfer path P2 becomes the main transfer path instead of the transfer path P1. On the other hand, if the data transferred through the transfer path P2 is received later by the transfer device 102 than the data transferred through the transfer path P1, duplication of data might happen when the transfer path P2 becomes the main transfer path instead of the transfer path P1. The missing of data and the duplication of data must be strictly avoided because of inducing a decline of quality of communications.
A data delay difference is, however, to occur depending on a difference in terms of transfer path length between the transfer paths P1 and P2, and a difference in status between the transfer paths P1 and P2. Such being the case, there are proposed some systems for obviating the data delay difference. FIG. 14 is a diagram showing a structure of the prior art transfer path control system containing a structural contrivance for obviating the data delay difference. FIG. 15 is an explanatory diagram of the transfer path control system shown in FIG. 14.
Referring to FIG. 14, the transfer devices 101, 102 are connected to each other through the transfer paths P1, P2, in which case the transfer device 101 stores a predetermined sequence number in a field called a J1 byte of an overhead of communications data (e.g., an SDH frame) transmitted through the transfer paths P1, P2 to the transfer device 102. Thereafter, the transfer device 102 through the transfer paths P1, P2, receives the data.
In the transfer device 102, each of detectors 105, 106 detects the content (the sequence number) of the J1 byte from the data transferred through the transfer paths P1, P2, and notifies a phase controller 107 of this sequence number. At this time, if a delay difference t (a difference between the sequence numbers) as shown in FIG. 15(a) occurs with respect to the same communications data between the transfer path P1 and the transfer path P2, the communications data are stored in a memory 108 and a memory 109, respectively. Then, the phase controller 107 reads the communications data simultaneously from the memories 108, 109 and transmits the data, whereby the same communications data are substantially simultaneously given to a selector 110. The delay difference t is thereby obviated. Thereafter, the selector 110 transmits only the communications data corresponding to the transfer path selected by the selector 110 itself. For example, if the transfer path P1 is selected, the selector 110 transmits only the data given from the memory 108.
There has existed in recent years a case where complicated transfer paths must be set in constructing the network system. For example, a new transfer path is build up in some cases for enhancing the reliability of the transfer paths, which have already been built up and operated. Alternatively, a new transfer path is build up as the case may be for altering the transfer paths that have already been built up and operated. In the case of building up the new transfer path, it must be necessary to try to see whether or not an accident happens when switching over the transfer path from the old one to the new.
There arise, however, the following problems inherent in the prior art of the transfer path control system illustrated in FIG. 14. That is, if a delay difference (a phase difference) between the transfer path P1 and the transfer path P2 is small, the communications data are stored in the memories 108, 109, and the same communications data are read therefrom simultaneous, thus obviating the delay difference (the phase difference). By contrast, if the delay difference (the phase difference) is large, capacities of the memories 108, 109 are limited, and hence one of the memories is saturated with the communications data before the same data are stored in the respective memories 108, 109, with the result that the missing of data occurs due to an overflow from the memory in some cases.
The prior art transfer path control system does not, however, have a construction for recognizing a result of switching over the main transfer path before the main transfer path is in fact switched over (before executing a switching operation of the selector 110 shown in FIG. 14). The operation of building up the new transfer path must be therefore conducted with great prudence in order not to cause the above problem, which is a troublesome part of the operation.
It is a primary object of the present invention to provide a transfer path control system capable of recognizing a result of switching before switching over a transfer path from a first transfer path to a second transfer path, and of, with this recognition, facilitating an operation of building up a new transfer path.
To accomplish the above object, the present invention adopts the constructions that follow.
According to a first aspect of the present invention, a transfer path control system comprises a first transfer device, and a second transfer device connected to the first transfer device through a first transfer path and a second transfer path for transferring the same data. The first transfer device comprises an index data adding unit adding index data to each piece of data transmitted to the first transfer path and the second transfer path. The second transfer device comprises a selection unit selecting one of the first transfer path and the second transfer path and, when receiving the same data through the first transfer path and the second transfer path, transmitting only the communications data corresponding to the selected transfer path, a first detecting unit detecting the index data from the communications data having arrived at the second transfer device through the first transfer path, a second detecting unit detecting the index data from the data having arrived at the second transfer device through the second transfer path, a phase difference detecting unit detecting a phase difference between the first transfer path and the second transfer path on the basis of respective pieces of index data detected by the first detecting unit and the second detecting unit, and a judging unit judging whether or not the one transfer path selected by the selection unit can be switched over to another transfer path in accordance with the phase difference detected by the phase difference detecting unit.
According to the first aspect of the invention, the judging unit judges using the phase difference whether or not the switching can be done, and it is therefore feasible to know a result of switching before the transfer path to be selected by the selection unit is switched over from the first transfer path to the second transfer path. This facilitates the operation of building up a new transfer path. In the transfer path control system according to the first aspect of the invention, the index data adding unit may add specified index data to the communications data, and the second transfer device may comprise a first time detecting unit detecting, as a first time, a time when the first detecting unit detects the specified index data from the data transferred through the first transfer path, a second time detecting unit detecting, as a second time, a time when the second detecting unit detects the specified index data from the data transferred through the second transfer path, a time difference calculating unit for obtaining a time difference between the first time and the second time, and a time difference storage unit storing the time difference calculated by the time difference calculating unit.
With this configuration, the time difference can be utilized as data when building up the sub-transfer path, whereby the operation of building up the transfer system in the sub-transfer path can be more simplified. Note that it may be another contrivance to judge by use of the time difference whether or not the instantaneously switching can be carried out.
In the transfer path control system according to the first aspect of the invention, the second transfer device may further comprise a switching control unit switching over the transfer path selected by the selection unit to another transfer path only when the judging unit judges that the switch-over can be carried out.
With this construction, the switchover can actually be implemented only when there is no possibility of causing a fault even by switching over the transfer path, so that the operation of building up the transfer path can be properly performed.
In the transfer path control system according to the first aspect of the invention, the switching control unit may operate in accordance with a switching command inputted to the second transfer device.
In the transfer path control system according to the first aspect of the invention, the second transfer device may further comprise a first buffer storing the data having arrived at the second transfer device through the first transfer path, a second buffer storing the data having arrived at the second transfer device through the second transfer path, and a capacity changing unit hanging a capacity of one of the first buffer and the second buffer in accordance with a phase difference detected by the phase difference detecting unit so that the same data stored respectively in the first buffer and the second buffer are substantially simultaneously given to the selection unit.
In the transfer path control system according to the first aspect of the invention, the second transfer device may further comprise a specifying unit specifying, when the same data are transmitted from the first transfer device simultaneously to the first transfer path and the second transfer path, the transfer path through which the same data arrives earlier at the second transfer device, a buffer for storing the data having arrived at the second transfer device through the transfer path specified by the specifying unit, and a capacity changing unit changing, if the same data as the data stored in the buffer arrives at the second transfer device through the transfer path which is not specified by the specifying unit, a capacity of the buffer in accordance with a phase difference detected by the phase difference detecting unit so that the same data having arrived at the second transfer device and the same data stored in the buffer are substantially simultaneously given to the selection unit.
According to a second aspect of the present invention, there is provided a transfer device connected to another transfer device through a first transfer path and a second transfer path for transferring the same data. The transfer device comprises a selection unit selecting one of the first transfer path and the second transfer path and, when receiving the same data from another transfer device through the first transfer path and the second transfer path, transmitting only the data corresponding to the selected transfer path, a first detecting unit detecting index data contained in the data transferred through the first transfer path, a second detecting unit detecting index data contained in the data transferred through the second transfer path, a phase difference detecting unit detecting a phase difference between the first transfer path and the second transfer path on the basis of respective pieces of index data detected by the first detecting unit and the second detecting unit, and a judging unit judging whether or not the one transfer path selected by the selection unit can be switched over to another transfer path in accordance with the phase difference detected by the phase difference detecting unit.
What can be exemplified a variety of transfer devices, e.g., an ATM transfer device used as a node in, e.g., B-ISDN (Broadband Integrated Service Digital Network). Further, the present invention can be applied to a frame relay transfer device.
According to a third aspect of the present invention, there is provided a transfer path control method of a transfer path control system comprising, a first transfer device, and a second transfer device connected to the first transfer device through a first transfer path and a second transfer path for transferring the same data, the second transfer device comprising a selection unit selecting one of the first transfer path and the second transfer path and, when receiving the same data through the first transfer path and the second transfer path, transmitting only the data corresponding to the selected transfer path. The transfer path control method comprises a step of adding index data to respective pieces of data transmitted by the first transfer device to the first transfer path and the second transfer path, a step of detecting the index data from the data having arrived at the second transfer device through the first transfer path, a step of detecting the index data from the data having arrived at the second transfer device through the second transfer path, a step of detecting a phase difference between the first transfer path and the second transfer path on the basis of respective pieces of index data detected, and a step of judging whether or not the one transfer path selected at the present time can be switched over to another transfer path in accordance with the phase difference detected.
The transfer path control method according to the present invention is capable of recognizing a result of switching before switching over the transfer path from the first transfer path to the second transfer path. Hence, it is feasible to facilitate the operation of building up the second transfer path while ensuring a reliability of the data transfer through the first transfer path.